Semiconductor laser apparatus, laser coupler, data reproduction apparatus, data recording apparatus and production method of semiconductor laser apparatus

ABSTRACT

There is provided a semiconductor laser apparatus capable of individually optimizing oscillations at a plurality of light emitting units fabricated on the single substrate in accordance with usages of each emitted laser lights. A plurality of cavities (laser diodes A and B), which correspond to the plurality of light emitting units, are fabricated on single substrate. And cavity lengths of the cavities are fabricated to different from one another.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor laser apparatus comprising cavities in correspondent with a plurality of light emitting units fabricated on the same substrate, and a laser coupler, a data reproduction apparatus and a data recording apparatus having the semiconductor laser apparatus, and a production method of the semiconductor laser apparatus.

2. Description of the Related Art

In recent years, an apparatus capable of recording and reproducing of a plurality of media such as CD (compact disk) and DVD (digital versatile disk) has been developed. When single apparatus is used to record/reproduce a plural types of media, the apparatus is required to have a system construction satisfying all the standards of media types included in the system. For example, at least two laser light emitting devices with different wavelengths have to be equipped in the same apparatus so as to perform recording/reproducing of both the CD and the DVD, that use laser lights with different wavelengths.

The device emitting laser lights with two different wavelengths may be realized by combining separate semiconductor laser devices emitting the two wavelengths and respective optical systems for the separate semiconductor laser devices. However, the combination of the separate devices and the optical systems may causes increase of a number of parts and a total cost of the apparatus, and prevent reduction of the apparatus size.

To resolve such disadvantages, a monolithic type semiconductor laser device had been developed. The monolithic type semiconductor laser device (so called two wavelength laser) has two active layers grown on the same substrate separately for emitting different wavelength lasers. FIGS. 10A and 10B are explanatory schematics illustrating a monolithic type semiconductor laser device. FIG. 10A is a plan view of the monolithic type semiconductor laser device. FIG. 10B is a cross sectional view showing a cross section taken on line X-X′ in FIG. 10A.

The semiconductor laser device may be produced, for example, by fabricating a n-GaAs buffer layer 2 a on a substrate 1 consisting of n-GaAs, and, a laser diode A emitting 780 nm band wavelength laser light and a laser diode B emitting 650 nm band wavelength laser light on the n-GaAs buffer layer 2 a. A separation between light emitting parts of the laser diode A and the laser diode B is less than 200 μm. For example, the separation may be set to less than 100 μm in many cases.

In the monolithic type semiconductor laser with the configuration described above, it is possible to keep a separation between the two laser lights into a smaller value with high precession since the active layers and the clad layers capable of emitting different wavelength laser lights are fabricated separately on the same substrate. Accordingly, an optical system at a subsequent stage may be shared, and it becomes possible to reduce a number of parts, a total cost of the apparatus, and a size of the apparatus.

SUMMARY OF THE INVENTION

However, there are some drawbacks in the semiconductor laser devices or apparatus described above despite of its advantages such as having a capability of sharing the same optical system in the subsequent stage and setting a smaller separation between the two laser lights with high precession, that are due to the fact that the laser diodes emitting different wavelength laser lights are fabricated separately on the same substrate. Namely, some of requirements from a system, which may be data reproducing/recoding apparatus using the multiple laser lights, may not be satisfied since cavity lengths in the semiconductor laser are fabricated the same.

For example, in the data reproducing/recording apparatus, there are requirements to optimize data reproduction/recording at 780 nm band laser light for the CD and at 650 nm band laser light for the DVD. However, all the cavity lengths are fabricated the same by cleavage since the both laser diodes are fabricated on the same substrate in the monolithic type semiconductor laser device described above. Accordingly, it is difficult to satisfy all the requirements for reproducing/recording of media using multiple wavelength laser lights.

Furthermore, a cavity of a laser diode may be fabricated to a longer length than necessary since a cavity length of one laser diode is determined by a cavity length of the other laser diode. Accordingly, a current consumption of the one laser diode is increased unnecessarily.

The invention was carried out to resolves such drawbacks. That is, in accordance with an embodiment of the present invention, there is provided a semiconductor laser apparatus comprising a plurality of cavities corresponding to a plurality of light emitting units on a substrate respectively, wherein the plurality of cavities have different cavity lengths.

According to the embodiment of the present invention, the semiconductor laser apparatus, comprising the cavities corresponding to the light emitting units on the same substrate and having different cavity lengths, may be optimized with requirements of a system such as data reproducing/recording apparatus employing the semiconductor laser apparatus therein since the cavity cavity lengths may be individually adjusted to different from one another.

Alternatively, the plurality of cavities in accordance with the present invention may be fabricated to have cavity lengths all less than a length of said substrate. Furthermore, one of the cavities in accordance with the present invention may comprise a three-element type compound semiconductor, and another of the cavities may comprise a four-element type compound semiconductor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic perspective view illustrating a semiconductor laser apparatus in accordance with an embodiment of the present invention;

FIG. 2A is a side view illustrating an example wherein the semiconductor laser apparatus in accordance with the embodiment is mounted on a photo detector substrate;

FIG. 2B is a plane view illustrating an example wherein the semiconductor laser apparatus in accordance with the embodiment is mounted on a photo detector substrate;

FIG. 3A is a cross sectional view illustrating a step of a production method of a semiconductor laser apparatus in accordance with an embodiment of the present invention;

FIG. 3B is a cross sectional view illustrating a step of the production method of a semiconductor laser apparatus in accordance with an embodiment of the present invention;

FIG. 3C is a cross sectional view illustrating a step of the production method of a semiconductor laser apparatus in accordance with an embodiment of the present invention;

FIG. 4A is a cross sectional view illustrating a step of the production method of a semiconductor laser apparatus in accordance with an embodiment of the present invention;

FIG. 4B is a cross sectional view illustrating a step of the production method of a semiconductor laser apparatus in accordance with an embodiment of the present invention;

FIG. 5A is a perspective view illustrating a step of the production method of a semiconductor laser apparatus in accordance with an embodiment of the present invention;

FIG. 5B is a cross sectional view illustrating a step of the production method of a semiconductor laser apparatus in accordance with an embodiment of the present invention;

FIG. 6 is a schematic plane view illustrating another embodiment of the present invention;

FIG. 7A is a schematic cross sectional view illustrating another embodiment of the present invention;

FIG. 7B is a schematic plane view illustrating the embodiment shown in FIG. 7A;

FIG. 8 is a schematic plane view illustrating another embodiment of the present invention;

FIG. 9A is a perspective view illustrating a laser coupler in accordance with an embodiment of the present invention;

FIG. 9B is a perspective view illustrating a laser coupler in accordance with another embodiment of the present invention;

FIG. 10A is a schematic plane view illustrating a semiconductor laser of the related art; and

FIG. 10B is a schematic cross sectional view illustrating the semiconductor laser shown in FIG. 10A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic perspective view illustrating a semiconductor laser device in accordance with an embodiment of the present invention. The semiconductor laser device of the present embodiment is so-called a monolithic type semiconductor laser device having cavities (active layers 4 a, 4 b) corresponding to a plurality of light emitting units fabricated on the same substrate 1, and particularly characterized by having different cavity lengths for the cavities.

In the semiconductor laser shown in FIG. 1, a laser diode A emitting laser light of 780 nm band oscillation wavelength for the CD and a laser diode B emitting laser light of 650 nm band oscillation wavelength for the DVD are fabricated on the same substrate 1.

The substrate 1 may consist of, for example, n-GaAs. In the laser diode A part, a n-clad layer 3 a comprising n-AlGaAs, an active layer 4 a comprising GaAs, a p-clad layer 5 a comprising p-AlGaAs and a cap layer 6 a comprising p-GaAs are fabricated layer by layer on a n-GaAs buffer layer 2 a. High resistance layers 7 a are fabricated on the p-clad layer 5 a at both sides in longitudinal direction leaving a striped gap between them, whereby realizing a gain guide type current stricture structure. On the top of the cap layer 6 a, a p-type electrode 8 a comprising Ti/Pt/Au multiple layers is fabricated. An n-type electrode 9 comprising AuGe/Ni/Au multiple layers is fabricated on the bottom side of the substrate 1. The n-type electrode 9 is shared for both the laser diode A part and the laser diode B part.

In the laser diode B part, a n-InGaP buffer layer 2 b, a n-clad layer 3 b comprising n-AlGaInP, an active layer 4 b comprising GaInP, a p-clad layer 5 b comprising p-AlGaInP and a cap layer 6 b comprising p-GaAs are fabricated layer by layer on the n-GaAs buffer layer 2 a. High resistance layers 7 b are fabricated on the p-clad layer 5 b at both sides in a longitudinal direction leaving a striped gap between them, whereby realizing a gain guide type current stricture structure. On the top of the cap layer 6 b, a p-type electrode 8 b comprising Ti/Pt/Au multiple layers is fabricated.

Among the laser diodes A and B, the laser diode B for the DVD has a cavity (the active layer 4 b) with a length (cavity length) determined by cleavage at the both edges. A length (cavity length) of a cavity (the active layer 4 a) of the laser diode A for the CD is determined by removing at one of its edges with using a dry process such as a reactive ion etching process (RIE). Accordingly, the cavity length of the laser diode B for the DVD may be adjusted to a suitable one for a DVD reproduction/recording apparatus (system) as well as the cavity length of the laser diode A for the CD may be adjusted to a suitable one for a CD reproduction/recording apparatus (system). The cavity length of the laser diode A can be independently determined without any restrain of the cavity length of the laser diode B.

FIGS. 2A and 2B are a side view and a plane view respectively showing an example of a photo detector substrate mounted with a semiconductor laser device in accordance with the present embodiment. In this example, the semiconductor laser device of the present embodiment is mounted on the photo detector substrate 10 with reversing the bottom side of the semiconductor laser device up. As described above, the cavity lengths of two laser diodes A and B are different in the semiconductor laser device of the present embodiment. Accordingly, one side of both laser diodes A and B are aligned while the other side are not whereby creating a step construction. In the present example, laser lights C1, C2 emitted from end faces at the side with the step construction are received at photo detectors 11 a, 11 b respectively. These photo detectors 11 a, 11 b are used, for example, to monitor laser light intensity.

The semiconductor laser device of the present invention enables to prevent interference of the laser lights C1 and C2 since the semiconductor laser device has the light emitting edge with the step construction so as to realize different emitting positions for the laser lights C1 and C2. A part of emitted laser light C1 spreads toward an outside wall of the laser diode B, and reflected thereon. Accordingly, the laser light C1 is prevented to reach the photo detector 11 b for receiving the laser light C2. In the present example, the laser lights C1 and C2 are accurately received by the photo detectors 11 a and 11 b, and whereby a precise monitoring is realized.

A Production method of the semiconductor laser device in accordance with an embodiment of the present invention will now be explained. Referring to FIG. 3A, a buffer layer 2 a, a n-clad layer 3 a, an active layer 4 a, a p-clad layer 5 a and a cap layer 6 a are fabricated on a substrate 1 layer by layer with using an epitaxial growth method such as a metal organic vapor epitaxial growth method (MOVPE). The buffer layer 2 a may consist of n-GaAs, for example. The n-clad layer 3 a may consist of n-AlGaAs, for example. The active layer 4 a may be constructed to have a multiple quantum well structure having GaAs layers, for example. The p-clad layer 5 a may consist of p-AlGaAs, for example. The cap layer 6 a may consist of p-GaAS, for example. The substrate 1 may consist of, for example, n-GaAs.

Next, as shown in FIG. 3B, a wet etching process such as non-selective type etching using sulfuric acid type solution and selective etching process for AlGaAs using hydrofluoric acid type solution are carried out after a part to become the laser diode A is covered by a resist (not shown in the figure) to be protected. The etching process removes all the layers fabricated above the n-clad layer 3 a at a part to be the laser diode B.

Next, as shown in FIG. 3C, a buffer layer 2 b consisting of, for example, n-InGaP is fabricated on the buffer layer 2 a of the laser diode B part and on the cap layer 6 a at a region beside the laser diode B part with using an epitaxial growth method such as the metal organic vapor epitaxial growth method. On the etched substrate, an n-clad layer 3 b, an active layer 4 b, a p-clad layer 5 b and a cap layer 6 b are fabricated layer by layer. The n-clad layer 3 b may consist of n-AlGaInP, for example. The active layer 4 b may be constructed to have a multiple quantum well structure having GaInP layers, for example. The p-clad layer 5 b may consist of p-AlGaInP, for example.

Next, as shown in FIG. 4 a, a wet etching process with using such as sulfuric acid type solution and selective etching process for AlGaAs using hydrofluoric acid type solution may be carried out to remove a part of the cap layer 6 b besides the laser diode B part after a part to become the laser diode b is protected by a resist (not shown in the figure). Furthermore, another wet etching process using such as phosphoric acid/hydrochloric acid type solution is carried out to remove the p-clad layer 5 b, the active layer 4 b, the n-clad layer 3 b and the buffer layer 2 b at a region besides the laser diode B part. Furthermore, another wet etching process using such as hydrochloric acid type solution is carried out to fabricate a trench reaching up to the buffer layer 2 a whereby the laser diodes are separated.

Next, as shown in FIG. 4 b, impurities are ion-implanted at surfaces of the p-clad layers 5 a, 5 b after protecting a part to become a current injection region of each laser diode with resist (not shown in the figure). Accordingly, the high resistance layers 7 a, 7 b are fabricated at the region exposed for the ion-implantation, and the gain guide type current stricture construction is realized.

Next, as shown in FIG. 5A, the high resistance layer 7 a, the cap layer 6 a, the p-clad layer 5 a, the active layer 4 a and the n-clad layer 3 a disposed at a part at one end of the laser diode A, which is used for the CD among the laser diodes A and B in the present example, are removed by a dry process such as a reactive ion etching (RIE) process. Accordingly, the cavity length of the laser diode A may be optimized. Alternatively, some of the part of the n-clad Layer 3 a may be left in another embodiment.

Next, as shown in FIG. 5B, p-type electrodes 8 a, 8 b are fabricated on the laser diodes A, B respectively by, for example, depositing multiple layers of Ti/Pt/Au on the cap layers 6 a, 6 b using a sputtering process. Furthermore, an n-type electrode 9 is fabricated on a side of the substrate 1 other than the side wherein the laser diodes A and B are fabricated.

After performing palletizing process, the semiconductor laser device as shown in FIG. 1 with the laser diodes A and B having different cavity lengths fabricated on the same substrate 1 is constructed. it is preferred to adhere dielectric films corresponding to oscillation wavelengths respectively at the end faces of the laser diodes A and B.

Another example of the present embodiment will now be explained. FIG. 6 is a schematic view (part 1) illustrating the instant example. According to a semiconductor laser of the present example, the cavity lengths of both the laser diodes A and B are optimized by removing a part of the end portion of one of the laser diodes A and B with using a dry process such as the RIE process as well as a barrier P is provided in between the laser diodes A and B by leaving a part remained by the dry process.

The laser lights C1 and C2 emitted from the end faces of the laser diodes A and B are completely separated by the barrier P. For example, when the laser lights C1 and C2 emitted from the end faces are radiated and received by photo detectors for intensity monitoring, a part of the laser light C1 emitted from the end face of the laser diode A, which is spreading toward a side of the laser diode B, is reflected by the barrier P. On the other hand, a part of the laser light C2 emitted from the end face of the laser diode B, which is spreading toward a side of the laser diode A, is reflected by the barrier P.

Accordingly, the laser lights C1 and C2 are completely separated by the barrier P, and received by the photo detectors without having any interference in between, whereby precise monitoring is realized. Furthermore, it enables simultaneous monitoring of the both laser lights C1 and C2 since there is no interference among the laser lights C1 and C2.

Furthermore, when the semiconductor laser device of the instant example is mounted on the photo detector substrate with reversing the substrate side of the semiconductor laser device up as shown in FIG. 2A, areas around emission portions of the laser lights C1 and C2 emitted from the laser diodes A and B are surrounded by the photo detector substrate, the substrate of the semiconductor laser device and the barrier P, shielded by three planes. Accordingly, the laser lights C1 and C2 are reflected by the surrounding surfaces and received efficiently by the photo detectors, and reception sensitivities of the photo detectors may be increased.

FIGS. 7A and 7B are a schematic side and plane views (part 2) of another example of the present embodiment. In the semiconductor laser device of the instant example, one of the laser diode parts A and B (the laser diode A for the CD use in this example) is fabricated to remove a middle part by the dry process (for example, by RIE process), and one of parts remained is used as a photo detector PDa for the laser diode A. In this example, a cavity length of the laser diode A is designated as L1 in the figures.

In the instant example, the photo detector PDa has the same construction as that of the laser diode A, and may be used as a light reception element for monitoring light intensity. Accordingly, both the laser diode A and the photo detector PDa may be fabricated at the same production step, and separate production steps are not required. Furthermore, the cavity lengths of the laser diodes A and B may be optimized in the same way as described in the previous example.

Furthermore, it is possible to apply coating on an end face of the laser diode A at a side facing the photo detector PDa with using, for example, a slant vacuum evaporation even when a middle part of the laser diode A part is removed (etched) as in the instant example.

FIG. 8 is a schematic view (part 3) illustrating another example of the present embodiment. In the semiconductor laser device of the instant example, middle parts of both the laser diode A part and the laser diode B part are removed by the dry process such as the RIE process. When the middle part of the laser diode A part is removed, some parts on both edges of the substrate are left remained, and one of the remaining parts is used as a photo detector PDa for the laser diode A. Similarly, when the middle part of the laser diode B part is removed, some parts on both edges of the substrate are left remained, and one of the remaining parts is used as a photo detector PDb for the laser diode B. The cavity length of the laser diode A, B is designated as L1, L2 in FIG. 8.

In the instant example, the photo detector PDa has the same construction as that of the laser diode A, and the photo detector PDb has the same construction as that of the laser diode B. Both photo detectors may be used as a light reception element for monitoring light intensity. Accordingly, each pair of the laser diode A and the photo detector PDa and the laser diode B and the photo detector PDb may be fabricated at the same production step, and separate production steps are not required. Furthermore, the cavity lengths of the laser diodes A and B may be optimized in the same way as described in the previous example.

An example of a laser coupler employing the semiconductor laser device in accordance with an embodiment of the present invention will now be explained. FIG. 9A is a schematic overview of a package of the laser coupler of the instant example, and FIG. 9B is a schematic overview of the laser coupler. The laser coupler may be used, as in one of the major applications, for an apparatus reproducing/recording data on an optical storage medium such as a CD and a DVD by radiating light thereon. In the instant example, the semiconductor laser device 100 in accordance with the present embodiment is mounted on a semiconductor block 130 in which a PIN photo diode 120 of a laser coupler 10 c is fabricated.

The laser coupler 10 c is mounted on a concaved portion of a first package member 20, and shielded by a second package member 30. The second package member 30 is transparent and may be made of glass material. For example, the semiconductor block 130, in which the PIN photo diode 120 is fabricated as the light reception element, is disposed on an integrated circuit substrate 110 which may be a substrate being cut-out from a monocrystal silicon. Furthermore, a monolithic type semiconductor laser device 100, in which the laser diodes A and B are fabricated on a common substrate as the light emission element, is disposed on the semiconductor block 130.

In the instant example, first photo diodes 160, 170 and second photo diodes 180, 190 are fabricated on the integrated circuit board 110, and a prism 200 is mounted on the first photo diodes 160, 170 and the second photo diodes 180, 190 so as to have a predetermined separation distance from the laser diodes A and B.

According to the laser coupler 10 c of the instant example, a part of a laser light F1 emitted from the laser diode A is refracted at a spectral plane 200 a of the prism 200 and radiated out along a predetermined emission direction through a radiation window fabricated at the second package member 30 to irradiate a target object such as an optical disk (for example, the CD) via optical elements (not shown in the figure) comprising such as a reflection mirror and an object lens.

A reflection light from the target object propagates along the reverse direction of the incident light to the target object, and returns to the spectral plane 200 a of the prism 200 along the reverse direction of the emitting direction out from the laser coupler 10 c. The returning light is focused at the upper surface plane of the prism 200, and falls onto the photo diode 160 at the upstream side and the photo diode 170 at the downstream side, both being disposed at the lower surface plane of the prism 200 and fabricated on the integrated circuit board 110.

Similarly, a part of a laser light F2 emitted from the laser diode B is refracted at a spectral plane 200 a of the prism 200 and radiated out along a predetermined emission direction through a radiation window fabricated at the second Package member 30 to irradiate a target object such as an optical disk (for example, the DVD) via optical elements (not shown in the figure) comprising such as a reflection mirror and an object lens.

A reflection light from the target object propagates along the reverse direction of the incident light to the target object, and returns to the spectral plane 200 a of the prism 200 along the reverse direction of the emitting direction out from the laser coupler 10 c. The returning light is focused at the upper surface plane of the prism 200, and falls onto the photo diode 180 at the upstream side and the photo diode 190 at the downstream side, both being disposed at the lower surface plane of the prism 200 and fabricated on the integrated circuit board 110.

The PIN diode 120 fabricated on the semiconductor block 130 may be divided into two regions for detecting laser lights emitted from the laser diodes A and B toward the rear direction. Results of the PIN diode 120 detection are used to measure intensities of the laser lights, and to perform an APC (auto power control) control to control drive currents of the laser diodes A and B so as to keep the intensities of the laser lights at constant values.

According to the laser couple 10 c employing the monolithic type semiconductor laser 100 in accordance with the present embodiment, a number of parts required for a optical pickup apparatus of the optical disk system using different wavelengths, for example, for the CD and the DVD. Accordingly, the laser coupler 10 c enables simplification of an optical system structure, and to provide easier assembling capability and reduce production costs. Furthermore, the semiconductor laser 100 in accordance with the present embodiment enables precise reproducing/recording operation since the cavity lengths of two laser diodes A and B are optimized for corresponding CD optical disk system and DVD optical disk system, respectively.

In all the embodiments described above, the semiconductor laser device emitting two laser lights is described as the example. Alternatively, the present invention may also be applicable to a semiconductor laser emitting more than three laser lights. Furthermore, the laser lights emitted from the semiconductor laser device in the embodiments described above. Alternatively, the laser lights emitted from the semiconductor laser device may have the same wavelength. Furthermore, the CD and the DVD are used as examples of the optical storage medium in the embodiments described above. Alternatively, other types of medium such as CD-R/RW and MD (mini disk) may be used as well in the present invention.

According to the present invention, the following effects may be achieved. The semiconductor laser with a plurality of light emitting units fabricated on the same substrate in accordance with the present invention enables optimization of every cavity length of the cavities corresponding to the plurality of the light emitting units, and simultaneously satisfying individual requirements of data reproducing/recording apparatuses using respective laser lights. Furthermore, the present invention enables to eliminate such a case wherein a cavity length of one laser diode have to be set a longer than necessary since a cavity length of the one laser diode is determined by a cavity length of the other laser diode, and to prevent increase of unnecessary current consumption. Furthermore, according to the present invention, the reproducing/recording performances for each of media in correspondent with each of the emitted laser lights may be promoted in the semiconductor laser device while advancing cost-cutting and downsizing of data reproducing/recording apparatus using the semiconductor laser. 

1-13. (canceled)
 14. A data recording apparatus having a semiconductor laser apparatus, wherein: said semiconductor laser apparatus comprises a plurality of cavities corresponding to a plurality of light emitting units disposed on a substrate, and at least one of said plurality of cavities has a cavity length different from another of said plurality of cavities, wherein said plurality of cavities is constructed to have cavity lengths all less than a length of said substrate. 